Cardiac

Cardiac Cycle Overview

• The cardiac cycle involves changes in pressure due to ventricular contractions.

Pressure Changes in the Ventricle

• Pressure rises quickly during isovolumetric ventricular contraction.

• All valves are closed during this phase:

  • Atrioventricular (AV) valves are closed.

  • Semilunar valves are also closed.

• Ventricular pressure increases as it contracts against closed valves.

• When ventricular pressure exceeds aortic pressure, the aortic valve opens, allowing blood flow into the aorta.

Blood Flow Dynamics

• As the ventricle continues to contract, pressure remains high.

• When the ventricle relaxes, the pressure begins to decrease.

• The aortic valve closes when ventricular pressure falls below aortic pressure.

• This ensures that blood can only be ejected when ventricular pressure is sufficient to exceed aortic pressure.

Right vs. Left Ventricle

• The right ventricle faces lower pressures in the pulmonary trunk, requiring less force to open the pulmonary valve.

• Right ventricular pressure during contraction is much lower than that of the left ventricle.

• If pulmonary pressure is elevated (e.g., in severe pulmonary disease), increased effort is needed to open the valve.

Structural Differences

• The left ventricle has thicker walls than the right ventricle, due to higher pressure exertion required to open the aortic valve.

• Comparison:

  • Left ventricle: Requires more force (like lifting a 50-pound weight)

  • Right ventricle: Requires less force (like lifting a 5-pound weight)

Conclusion

• Understanding how ventricular pressure changes during the cardiac cycle is essential for comprehending heart function and diagnosing potential cardiovascular issues.